1. Field of the Invention
The present invention relates to switch interlock apparatus, such as are used with switch panels, like electrical breaker switch panels, wherein the switches are arrayed in pairs.
2. The Prior Art
Switching apparatus, such as breaker switch panels, that have switches that are arrayed in pairs, are known. Typically, the individual switches in such switch apparatus are laid out in such a manner that switches that are connected to related circuits are arranged in horizontal pairs, wherein in order to accomplish a particular switching operation, it is either desirable or absolutely necessary that one switch be flipped (opened or closed) before a second switch of a functional pair is flipped (closed or opened). Together, such a switch functional pair is often referred to collectively as a “break-before-make” switch.
One such environment in which such “break-before-make” switch combinations are used is a transfer switch panel. Transfer switches are switches or groups of switches that are used to convert a powered circuit, such as a residential or commercial structure, from one source of electrical current, to another source of current. One typical example is a residential structure that is provided with an independently powered back-up electrical generator. A transfer switch or switch panel will be connected to the household circuits, the utility power connection, and to the input from the generator.
If the transfer switch is manual, upon failure of the utility power, an operator will flip the transfer switches, disconnecting the utility current source from the household circuitry and connecting the back-up generator to the household circuitry. The generator is then started (or may have already been started) and back-up current is supplied to the residence.
If the transfer switch is of the automatic type, it will monitor various characteristics of the utility power being supplied, and if one or more of the characteristics falls below a predetermined numerical value, a similar sequence of switches will be automatically flipped through an automated mechanism, and the generator (if provided with an electric starter circuit) will be automatically started.
For manual transfer switches, typically, physically separate switches are used for each functional switch pair, in two columns of switches. Typically, such switches are biased, so that once a switch handle has reached top dead center, any slight deflection from that position, will cause the switch to continue to the full switched position on that “side” of top dead center, unless otherwise restrained.
The reason that separately acting switches are used is to ensure that the utility current circuitry is disengaged before the power is applied, to prevent power from being fed back into the utility current source circuit, potentially causing substantial damage to utility equipment and/or personal injury. In addition, typically, the polarities of the switches in the respective columns are reversed. For example, in a switch panel having two columns of switches, the individual switches of one column of switches must be flipped first before the corresponding individual switches of the column of switches can be flipped. For example, in the left-hand column, which may be the switches for connecting the back-up generator circuit to the household circuit, the “ON” positions for the switch handles will be on the right and the “OFF” positions for the switch handles will be on the left. In the right-hand column, which may be the switches for connecting the line/utility circuit to the household circuit, the “OFF” positions will be to the right, and the “ON” positions will be to the left. In such an arrangement, the switches on the right must be flipped before the corresponding ones on the left can be safely flipped. However, there may be a tendency for an operator to make a single left-to-right hand movement would flip all the left column switches from “ON” to “OFF”, and then flip all the right column switches from “OFF” to “ON”. In such a situation, the order of switching would be improper, and could lead to damage or personal injury.
Therefore it has been determined that it is not only desirable but necessary to ensure that the switches engaging the generator to the household circuit cannot be flipped, before the line/utility is disconnected from the household circuit. By advantageously connecting the switch handles together, it is ensured that if a generator switch is flipped, the corresponding line/utility switch will be flipped first.
Interlock devices for connecting the handles of such functional pairs of switches are known. One such device is disclosed in Flegel, U.S. Pat. No. 6,031,193. The apparatus that is disclosed in the Flegel '193 patent comprises two flat metal plates that are connected together by a “U”-shaped metal piece that has two upturned ends. The bottom of the “U” has a series of holes through which screws may be passed, and in turn, passed through holes in the ends of the two flat metal plates (for adjustability). The distance between the upturned ends (stops) of the U-shaped metal piece is about the distance between the inside faces of the switches, when one is in the “OFF” position and the other is in the “ON” position. The interlock is assembled in place, with the two flat bars being slid through recesses or apertures beneath the cross bars of the individual opposed switch handles, and then connected to each other via the “U”-shaped component. Screws are placed in holes in the opposite ends of the interlock (to the outside of the two switches), the ends of which are intended to ride in slots (presumably already provided in the face of the switch panel) between the pairs of tandem switches, as an additional guide arrangement. The stops on the U-shaped metal piece are spaced so that when a switch in the “OFF” position is being moved toward the “ON” position, the switch in the “ON” position is moved to top dead center and then into its over-center position and switches, under bias, to “OFF” before the first switch arrives at its respective “ON” position.
However, such a design has several potential limitations. First, it must be assembled in place from component parts, thus making it somewhat awkward and labor intensive to install. Second, it requires that each of the switch handles actually be a tandem (side-by-side) handle, so that there is a gap or hole, through which the main bar of the interlock has to be passed. Third, the design requires the presence of a groove or rail, into which the ends of the screws are received, to act as a guide for the reciprocating movement of the interlock apparatus.
It would be desirable to provide a switch interlock apparatus that has a simplified structure that does not require assembly of numerous component parts.
It would also be desirable to provide a switch interlock apparatus that can be pre-assembled prior to mounting to a switch panel.
It would also be desirable to provide a switch interlock apparatus that does not depend upon structural features of the switch panel to which it is being mounted, such as a groove or rail, for functionality.
These and other desirable characteristics of the present invention will become apparent in view of the present specification, including claims, and drawings.